Effect of oestrogen treatment on gonadotroph function in adult male rats

The effect of oestradiol-17 beta on the hypothalamo-pituitary axis of intact adult male rats was studied. A single injection of oestradiol did not change the serum LH response to gonadotrophin-releasing hormone (GnRH) 48 h or 7 days after the injection, while administration of oestrogen over 66 days suppressed basal serum LH to less than 3.1 micrograms/l and did not enhance the LH response to GnRH at any time. Treatment of ovariectomized rats with oestradiol capsules, however, enhanced the LH response to GnRH on days 3 and 14 of the treatment as compared with the control group (P less than 0.02 and P less than 0.05 respectively). Long-term treatment with oestradiol suppressed intrapituitary LH and FSH contents as well as pituitary GnRH receptors (P less than 0.0004, P less than 0.005 and P less than 0.001 respectively), whereas serum and intrapituitary prolactin levels were increased. To exclude the possible lactin levels were increased. To exclude the possible inhibitory effect of hyperprolactinaemia on LH were treated with bromocriptine. This prevented the rise in serum prolactin, but failed to enhance the LH response to GnRH. Neither short- nor long-term treatment with oestradiol given under conditions shown to be effective in female animals stimulated the hypothalamo-pituitary-gonadotrophin axis in adult male rats.